Low-pressure absorption refrigeration



Patented June 6, 1950 UNITED STATES PATENT OFFICE LOW-PRESSURE ABSORPTION REFRIGERATION Clifford E. Skomp, Evansville, Ind., assignmto Servei, Inc., New York, N. Y., a lcorporation of Delaware Application April 8, 1947, Serial No. '139,999

(ci. sz-11s) 9 Claims.

they accumulate. It is, therefore, desirable that these gases be removed from those parts of an absorption refrigerating system in which their presence adversely affect the operation of the system. However, it has been found in practice that the presence of a limited amount of noncondensable gas in certain parts of a low pressure Yabsorption refrigerating system is desirable. In

the generator, for instance, non-condensable gases form vapor nuclei which reduce superheat and thereby promote quiet boiling of the refrigerant-absorbent solution. Also, if a fall tube is used for purging the system of non-condensable gases, the gases act as a cushion for vapor collapsing in the fall tube. system is stripped of non-condensable gases, the purge pump is apt to become noisy due to the collapsing of refrigerant vapor between slugs of absorption solution.

It is, therefore, an object of this invention to provide an improvement in an absorption refrigerating system, whereby such system is purged of any excess of non-condensable gases while maintaining a limited amount of such gases in circulation in the system.

The invention together with its objects and advantages will be more clearly understood from the following detailed description taken in connection with the accompanying drawing, in which the single iigure is a view diagrammatically illustrating a refrigerating system embodying the invention.

For purposes of illustration, I have incorporated my invention in a two-pressure absorption refrigerating system like that disclosed in U. S. patent to A. R. Thomas, No. 2,384,860, granted September 18, 1945. A system of this type operates at low pressures and includes a generator or vapor expeller I0, a condenser II, an evaporator I2 and an absorber I8 which are interconnected in such a manner that flow of fluid between the high and low pressure sides of the system is regulated by liquid columns. The disclosure in the aforementioned Thomas patent In other words, if the application, and, if desired, reference may be made thereto for a detailed description of the refrigerating system.

The generator includes an outer shell IS within which are disposed a plurality of vertical riser tubes I6 having the lower ends thereof connected to receive liquid from an inlet chamber I1 and the upper ends extending into and above the bottom of a separating vessel I8. A space I8 within shell I5 forms a chamber to which steam is supplied through a conduit from a suitable source of supply, so that full length heating of may be considered as being incorporated in this the tubes I6 is effected. A vent 2I is provided atthe upper end of shell I5, and a conduit 22 is connected to the bottom part of the shell for draining condensate from the space I9.

The system operates at a partial vacuum and contains a water solution of refrigerant in absorbent liquid, such as, for example, a water solution of lithium chloride, lithium bromide or a mixture of the two. When steam is supplied through conduit 20 to space IS at atmospheric pressure, heat is supplied to tubes I6 for expelling water vapor fromsolution. The residue adsorption liquid is raised by gas or vapor-lift action. The water vapor discharged from the upper ends of the tubes or risers I6 separates from the raised absorption liquid in the vessel I8 and iiows through a conduit 28 into condenser II wherein the vapor is condensed. The condensate formed in the condenser flows through a U-tube 24 into a flash chamber 25 and from the latter through a tube 26 into evaporator I2.

The evaporator includes a plurality of horizontal banks of tubes 21 disposed one above the other and having heat transfer fins 28 secured thereto to provide a relatively large heat transfer surface. The liquid refrigerant flowing to the evaporator is divided in any suitable manner for iiow through the uppermost bank of tubes 21. For example, the dividing of liquid may be eiected by a liquid distributing trough 29 into which the liquid ows from the tube 26. The liquid refrigerant ows in successively lower tubes through suitable end connections which are open to permit escape of vapor from the tubes.

The liquid refrigerant supplied to tubes 21 evaporates therein to produce a refrigerating or cooling effect with consequent absorption of heat from the surroundings, as from a stream of air owing over the exterior surfaces of the tubes 21 and fins 28. The vapor formed in tubes 21 passes out into end headers 30 which are connected at their lower ends to absorber I3. Any vapor formed in iiash chamber 25 passes through a conduit 3| into one of the headers 3l and mixes with vapor formed in the evaporator I 2,-s`o that disturbances in the evaporator due to vapor ashing of incoming liquid are avoided.

In absorber I3 refrigerant vapor is absorbed into absorption liquid entering through a conduit 32. The entering absorption liquid flows into a vessel 33 in which liquid is distributed laterally with respect to a plurality of vertically disposed pipe banks 34 arranged alongside of each other. The liquid ows from vessel 33 througlrconduits 35 into a plurality of liquid holders and distributors 36 which extend lengthwise of and above the uppermost branches of the pipe banks 34, Absorption liquid is siphoned over the walls of the liquid holders 36 onto the uppermost pipe sections. Liquid drips from each horizontal pipe section onto the next lower pipe section, so that all of the pipe sections are wetted with a iilm of liquid. Absorption liquid enriched in refrigerant flows from absorber I3 through a conduit 31, an inner group of passages in a liquid heat exchanger 38, a conduit 39, a stabilizing vessel 40, and a. conduit 4I into the inlet chamber I1 of the generator. Water vapor is expelled out of solution in the generator by heating, and liquid is raised by gas or vapor-lift action in riser tubes I6, as explained above. r

The absorption liquid in vessel I8, from which refrigerant has been expelled from solution, ows through a conduit 42, another group of passages in liquid heat exchanger 38 and conduit 32 into the upper part of absorber I3. This circulation of absorption liquid is effected by raising liquid in the vertical riser tubes I6 by vapor-lift action, so that liquid can flow from generator I to absorber I3 and return from the latter back to the generator by force of gravity.

The upper part of vessel 40 is connected by a conduit 43 to vessel I8, so that the pressure in vessel 40 is equalized with the pressure in the upper part of generator I0 and condenser II. Vessel 40 is of suiiicient volume to hold the liquid differential in the system and is of suincient cross-sectional area that the liquid level therein does not appreciably vary, so that a substan tially constant reaction head is provided for lifting liquid in generator I0.

The heat liberated with absorption of water vapor in absorber I3 is transferred to a cooling medium, such as water, which flows upward through the vertically disposed pipe banks 34. The cooling medium enters the lower end of the pipe banks through a conduit 44 and leaves the upper end of the pipe banks through a conduit 45. Conduit 45 is connected to condenser II so that the same cooling medium is utilized to effect cooling of both the condenser and the absorber. From condenser II the cooling medium flows through a conduit 46 to waste, or to a cooling tower, not shown.

During operation of the refrigerating system, non-condensable gases may collect in both the high and low pressure sides of the system. The non-condensable gases collecting in the high pressure side of the system, that is, the generator II) and condenser II, are carried to the dead or far end of the condenser in the bottom part thereof by the sweeping eiect of the refrigerant vapor flowing into the condenser. Since the noncondensable gases are swept to the bottom part of the condenser, the U-tubel 24 is effectively utilized to ltransfer such gases from the condenser to the evaporator by providing a, trap 41 therein. Trap 41 traps gas in the down leg of condensable gases conduit 52. A screen, not

, 4 tube 24 between slugs of liquid intermittently siphoned from the trap. 'Hence, the liquid refrigerant owing through tube 24 to the evaporator carries with it the non-condensable gases collecting in the condenser and generator.

The non-condensable gases in the low pressure side of the system, that is, in the evaporator I2 and absorber I3, are carried to the bottom' center part of the absorber by the sweeping action of the refrigerant vapor entering the top of the absorber through headers 30. In order to localize the nonin a relatively small space, such gases are withdrawn from the bottom part of absorber I3 through a-conduit 50 to the top of an auxiliary absorber 5I. A small portion of the absorption liquid owing toward the upper part of absorber I3 in conduit 32 .is diverted into a shown, removes any foreign matter in the diverted liquid tending t0 clog a flow-restricting device 54, and the restricting device in turn limits the rate at which liquid is diverted into conduit 52 from the main stream of absorption liquid flowing in conduit 32. The auxiliary absorber is provided with horizontal plates, not shown, over which the diverted absorption liquid flows.

While the gases withdrawn from absorber I3 through conduit 50 into auxiliary absorber 5I are for the most part noncondensable, these gases are not suiliciently localized in the bottom of the main absorber I3 and tests have shown that refrigerant vapor accompanies the non-condensable gases withdrawn from the main absorber. For this reason the gases withdrawn from absorber I3 are brought into intimate contact with the diverted absorption liquid in the auxiliary absorber, whereby the refrigerant vapor accompanying the non-condensable gases is absorbed into the absorption liquid. The heat liberated with absorption of refrigerant vapor in the auxiliary absorber is transferred to the cooling medium flowing through a coil 55 connected between the inlet 44 and outlet 45 of the cooling system of the main absorber. The absorption liquid and gases both ow downwardly in intimate contact with each other in the auxiliary absorber and the gases arrive at the bottom part of the auxiliary absorber substantially stripped of refrigerant vapor. y

The liquid flowing by gravity to the bottom part of the auxiliary absorber enters the upper end of a conduit 51 until the conduit is closed with liquid and sealed from the gases in the bottom part of the auxiliary absorber. When the liquid level rises sufficiently in the upper curved or bent portion of conduit 51. the small quantity of liquid within the open end is siphoned past the bend into the downwardly depending straight portion thereof. When liquid is siphoned from the upper curved end of conduit 51, the liquid level falls in the bottom part of the auxiliary absorber below the upper open end of conduit 51, so that non-condensable gases pass into the upper bend or curved part of this conduit. The liquid level in the bottom' part of the absorber 5I again rises to close and seal the upper end of conduit 51, and, when the liquid level again rises suiciently, a small quantity of liquid is once more siphoned into the downwardly depending straight portion of conduit 51. In this way small quantitiesk of non-condensable gases are withdrawn from the bottom part of auxiliary absorber 5I and trapped between successive slugs of liquid formed at the upper curved or bent portion of the conduit 51. Conduit'51, which may be referred to as a fall tube pump or primary purge pump, is of such size that now of liquid is not appreciably restricted, however, the internal diameter thereof is such that gas and liquid cannot pass each other while flowing downwardly through the conduit. The lower end of tube 61 is connected at 58 to the bottom part of vertical tube 48, and the latter is connected by a conduit 59 to the bottom part of conduit 31 through which absorption liquid ows from the bottom or outlet of absorber I3- toward generator I9. The upper end of conduit 48 opens into a purge reservoir 49, which reservoir is provided with an evacuating pump 68. A conduit 8|, provided with a valve 62, connects the evacuating pump to the reservoir.

As stated at the outset of this application, it is often desirable that a small amount of non-condensable gases be retained in certain types of refrigerating systems. In the particular system illustrated, the circulation o a small amount of non-condensable gases promotes quiet boiling in the generator of such systems. Also, if a U-tube, as shown, is used to control the ilow of liquid refrigerant from the condenser to the evaporator. the circulated non-condensable gases act as a cushion for refrigerant vapor collapsing in such U-tube, thereby reducing the noise which would otherwise be produced by this collapsing of vapor. Furthermore, if a fall tube is used as the purge pump, should the system be stripped of non-condensable gases, there would also be some collapsing of vapor bubbles by the slugs of absorption solution in the fall tube, which, in the absence of non-condensable gases, would produce noise in the fall tube. In accordance with this invention, I provide a second purge pump, which may be termed an auxiliary purge pump, and which is designated generally by reference character 63. This auxiliary purge pump includes a U-tube having one leg 64 opening into a sump 65 provided in the lower portion of separating vessel I8, and a second leg 66 opening into the bottom of purge reservoir 49 and provided with an enlarged portion 61, which enlarged portion may be termed a receiver. In order to protect conduit 64 from foreign matter, a screen 68 is located at the inlet of sump 65. A fall tube 69, provided with a downwardly bent portion 18 at its upper end, is connected between receiver 61 and the inlet chamber I1 of the generator. Legs 64 and 66 of the U-tube may be provided with metering orifices, not shown, to control the flow of absorption solution and non-condensable gases therethrough. In the absence of a metering orifice inleg 64, the conduit 4which forms fall tube 69 should be slightly larger in internal diameter than the conduit which forms leg 64. This is necessary in order that absorption solution may ow from receiver 61 through fall tube 69 faster than the solution is supplied to the receiver by the leg 64 of the U-tube.

In operation, non-condensable gases are withdrawn from the absorber I3 through conduit 50, auxiliary absorber 5I and primary fall tubel51 into the bottom of tube 48, and through tube 48 into purge reservoir 49. From the purge reservoir small amounts of non-condensable gases flow through conduit 66 into receiver 61. Simultaneously with this operation a small amount of absorption solution ows from sump 65 through conduit 64 into receiver 61, from whence the absorption solution overilows through the bent portion of the auxiliary fall tube 69 and through this fall tube to the inlet chamber I1 o! the gerierator. During this operation, after the liquid level builds up in receiver 61 to the point of overilow through the bent portion 1li of the auxiliary fall tube this liquid is siphoned in small quantities out of the receiver 61 and the liquid level in the receiver is thereby lowered to the point that the open end o! the fall tube is exposed and noncondensable gases ow from receiver 61 into the bent portion 19 of the fall tube. In this manner non-condensable gas is trapped between slugs of absorption solution in fall tube 69, which non-condensable gas is delivered along with the slugs of absorption solution into inlet chamber I1 of the generator. Non-condensable gases introduced into the inlet chamber of the generator pass directly into the riser tubes I6, wherein the gases form vapor nuclei which reduce superheat and promote quiet boiling of the solution in the generator. The mixture of refrigerant vapor, non-condensable gas and absorption solution spurts from the top of the riser tubes into separating vessel I8. Due to the splashing of the absorption solution against the banles in the separating vessel, some of the non-condensable gas will be entrained as small bubbles in the solution, and part of this mixture of absorption solution and small bubbles of non-condensable gas will flow through conduit 64, receiver 61 and fall tube 69 back to the bottom of the generator. The remainder of this mixtue of absorption solution and small bubbles of non-condensable gas will flow from the separating vessel through conduit 42, heat exchanger 38 and conduit 32 into the absorber I3. Also, some of the non-condensable gas which passes upwardly through riser tubes I6 and into separating vessel I8 will travel through conduit 23 with refrigerant vapor into the condenser II, and from there into U-tube 24. In passing through the U-tube non-condensable gas will act as a cushion for refrigerant vapor collapsing in this tube thereby reducing the noise formed by this vapor collapsing. As explained earlier in this application, this non-eondensable gas passes along with liquid refrigerant from U- tube 24 into the evaporator I2 and from there into the absorber I3, from whence said gas is withdrawn through conduit 59, auxiliary absorber 5I primary fall tube 51 and conduit 4 8 into purge reservoir 49. It is to be noted that the auxiliary purge pump 69 must pump only small amounts of non-condensable gas. In other words, the auxiliary purge pump must be considerably less eicient than the primary purge pump 51, otherwise an excess of non-condensable gas would be circulated continuously through the system. Should non-condensable gases accumulate in the system in an amount greater than that desired for continuous circulation therethrough such gases are withdrawn from time to time by the evacuating pump 69|.

Having thus described my invention, I wish it understood that I do not desire to be limited to the specic structure illustrated and described, for obvious modifications may occur to a person skilled in the art.

What is claimed is:

1. An absorption refrigerating system of the two-pressure type including a generator, a condenser, an evaporator, an absorber and conduits interconnecting said elements for flow of a refrigerating medium and an absorption solution, a primary purge pump for withdrawing non-condensable gases from said refrigerating system, a reservoir for receiving and storing said withdrawn non-condensable gases, and an auxiliary purge pump connected to the reservoir and one of the conduits for withdrawing a portion of the stored non-condensable gases and delivering them for :dow through said refrigerating system.

2. An absorption refrigerating system including a generator, a vapor separator, a condenser, an evaporator, an absorber and conduits interconnecting said elements for ow of a reirigerating medium and an absorption solution, a primary purge pump for withdrawing non-condensable gases from said system, a reservoir for receiving and storing said withdrawn non-condensable gases, a conduitfor iiow of absorption solution from said vaporA separator to said generator, and an auxiliary purge pump in said last-named conduit and connected to said reservoir for withdrawing a portion of the stored non-condensable gases and delivering them into the absorption solution iiowing to said generator.

3. An absorption refrigerating system including a generator, a vapor separator, a condenser, an evaporator, an absorber and conduits interconnecting said elements for ow of working media therethrough, a purge pump for withdrawing non-condensable gases from said system, a reservoir for receiving and storing said withdrawn non-condensable gases, said conduits including a path of ow of vapor from said vapor separator to said condenser, a path of flow of absorption solution from said vapor separator to said generator and a path of ilow of absorption solution from said`vapor separator to said absorber, and means connected to said reservoir and utilizing the iiow of absorptionl solution in the path of flow from said vapor separator to the generator for delivering stored non-condensable gases to said generator from whence said gases flow through each of said paths of iiow.

4. A refrigerating system including a, liqueer, an evaporator and conduits interconnecting said elements forming circuits for iiow of working media therethrough, a purge pump for Withdrawing non-condensable gases from a portion of said refrigerating system, a reservoir hermetically connected to the system and forming a part thereof for receiving and storing said withdrawn non-condensable gases out of the working media circuits, and means connected to the reservoir for withdrawing gases from storage at a predetermined rate and circulating them through the refrigerating system whereby to maintain a controlled quantity of non-condensable gases in circulation in the system.

5. A heat-operated refrigerating system including a generator, a liqueiier, an evaporator and conduits interconnecting said elements forming circuits for iiow of working media therethrough. a purge pump for withdrawing noncondensable gases from a portion of said refrigerating system, a reservoir closed to the atmosphere and forming a part of said system for receiving and storing said withdrawn non-condensable gases out of the working media circuits, and means connected to the storage reservoir for withdrawing a portionY of the stored non-condensable gases and injecting them into the working media iiowing through the system.

6. An absorption refrigerating system including a generator, a condenser, an evaporator, an absorber and conduits interconnecting said elements for ilow oi' a refrigerating medium and an absorption solution, a purge pump for withdrawing non-condensable gases from said system, a reservoir hermetically connected to the system and forming a part thereof for receiving and storing said withdrawn non-condensable gases out. of the working media circuits, and means connected to the reservoir and to the generator for withdrawing a portion of the stored noncondensable gases and vdelivering them to the generator of said syste e 7. In the art of refrigeration through the agency of a heat-operated refrigerating system. which system includes a generator, a liquefler, an evaporator and `conduits interconnecting said elements for flow of working media therethrough,

that improvement which comprises withdrawing non-condensable gases from certain parts of said system, storing the withdrawn non-condensable gases in the system but out of the path of flow of working media, and withdrawing at least a portion of the non-condensable gases from storage and circulating the withdrawn gases through the path of ilow of working media.

8. In the art of refrigeration' through the agency of an absorption refrigerating system of the two-pressure type, which system includes a generator, a condenser, an evaporator, an absorber and conduits interconnecting said elements for iiow of working media therethrough, that improvement which comprises withdrawing noncondensable gases from certain parts of said system, storing the withdrawn non-condensable gases in the system but out of the path of ow of working media, and then withdrawing noncondensable gases from storage at a predetermined rate and injecting them into the working media circulating in the system whereby to provide a controlled amount of non-condensable gases in circulation in the system.

9. In the art of refrigeration through the agency of an absorption refrigerating system of the two-pressure type, which system includes a generator, a condenser, an evaporator, and absorber and conduits interconnecting said elements for iiow of a refrigerating medium and an absorption solution therethrough, that improvement which comprises withdrawing non-con- REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 942,367 Dyer Dec. 7, 1909 1,679,439 Munters Aug. 7, 1928 1,710,438 Sweeney Apr. 23, 1929 2,320,349 Cropper June 1, 1943 *was 

